As explained in said parent application, the maintenance and monitoring of fluids in vehicles, wind turbines, engines, pumps, weapons and machinery and the like (all hereinafter, for convenience, generically referred to as “machinery”) is vital to ensuring reliable operation. While there is no single sensor available that can monitor all fluids simultaneously, due to the wide variation in composition and fluid failure mechanisms, a suite of networked, miniaturized onboard vehicle fluid sensors can be envisioned for continuous, in-situ monitoring of fluid degradation. In the case of brake fluid and hydraulic fluid, the main mechanism for fluid degradation is humidity absorption, excess particulates (metal and sand), and solvent contamination. In-line hydraulic fluid humidity sensors are commercially available from several sources. In the case of engine coolant, increased acidity leads to corrosion in internal engine components. The pH monitoring of coolant is beneficial, and could be implemented using commercial sensors (e.g. Durafet III pH electrode from Honeywell), which could be packaged for use in machinery by a third party. In the case of engine oil, as referenced in said patent application there are dielectric, viscosity, conductivity, chromatic modulation, x-ray fluorescence, infrared and other sensors used to detect changes in the observable fluid properties. Several sensor systems are available which examine changes in dielectric permittivity and viscosity of oil, as are vehicle-specific software systems that predict oil failure based on past driving conditions (deployed by General Motors). There are to date, however, no commercially-available sensors that provide a rigorous, real-time detection of the most fundamental chemical mechanism of engine lubricating oil failure,—the formation of free radicals by the breakdown of long hydrocarbon molecular chains in oil. Only the overall results stemming from these free radical-induced changes have heretofore been monitored in-situ, but not the direct detection of the free radicals themselves, and not by microwave ESR spectrometer designed for such free radical direct detection.
As stated in said parent application, numerous other systems have, however, before been developed by auto manufacturers and others for improved automotive fluids management. Researchers have prototyped the use of viscosity sensors, dielectric sensors, chromatic sensors (sensing color changes), oil pH sensors, miniature Fourier transform infrared spectrometers (FTIR) and x-ray fluorescence sensors, sensors of magnetic particles as of iron-derived and transition metal particles and combinations thereof. General Motors employs a computer model, which uses the vehicle driving history, environmental conditions (temperature, humidity) and maintenance history to predict when the oil must be changed, but without specialized sensors, although detailed data from millions of miles of road tests was required to create this computer model. The present invention, however, based on said parent application, differs from these approaches in a fundamental way: namely, directly in situ sensing by microwave ESR sensors the molecular changes that occur in oil as a result of breakdown of the lubricant.
Onboard monitoring of lubricant degradation provides a reduction in engine wear and reduced maintenance costs for the end-user. The net economic benefit of this optimized maintenance schedule can be very large. In the United States, over one billion gallons of motor oil are used each year; thus any reduction in oil usage can have a significant impact. In civilian automotive applications, engine oil is typically changed every 3000-7500 miles, while coolant, brake fluid and automatic transmission fluid are changed every 30 k-50 k miles. The economic benefit to the end user of optimized engine oil management may be greater than for other automotive fluids, both in reduced fluid costs and in reduced wear of engine components.
In said parent application, novel tunable microwave-frequency swept ESR miniaturized spectrometers are disclosed for such direct sensing of such molecular changes resulting from the lubricant breakdown during vehicle usage. The structure involved the varying or sweeping of the RF frequency of a cavity resonator by varying the gap of an external capacitance, as by deforming a piezoelectric element positioned along the top wall of the cavity resonator. While useful in some applications, such structures are subject in other applications to serious vibrational noise, now eliminated by the structure of the present invention through the use of a fixed frequency RF cavity resonator and a preferably audio-frequency swept internal magnetic field modulation of a uniform slowly varying magnetic field.
Neither the parent application nor this improvement application, however, involves the first use of an ESR spectrometer, though they are believed to be the first adapted and described for the purpose of the specific invention—namely a miniaturized microwave ESR spectrometer for in situ use, measuring directly the molecular changes that occur in oil and the like as a result of breakdown during usage.
Prior ESR Spectrometers in General
Microwave electron spin resonance spectrometers of a myriad of types have heretofore been developed for uses other than that of the present invention. U.S. Pat. No. 4,803,624 issued Feb. 7, 1989, for example, discloses an electron spin resonance spectrometer operating at frequencies in the range of 2 to 3 GHz, using loop-gap resonators at these frequencies in a preferred embodiment. This spectrometer uses a circulator to measure the reflected microwave power from the resonator, the same as in most commercially available electron spin resonance spectrometers. Microwave circuit components, for example an isolator, circulator, power dividers, variable attenuator, and directional couplers, are arranged in a microwave bridge connected by microstrip transmission lines. External components, such as the microwave source and loop-gap resonator, are connected via SMA coaxial connectors. The microwave circuit construction uses microstrip transmission line connections formed by RF circuit boards laminated onto an aluminum backplane. This patent suggests the use of Sm—Co based permanent magnets and auxiliary field sweep coils, but does not present detailed embodiments of the magnet.
Another prior art microwave electron spin resonance spectrometer is disclosed in U.S. Pat. No. 5,233,303, issued Aug. 3, 1993. The spectrometer operates in the 2 GHz frequency range, and is intended for portable use. The design similarly uses a circulator to measure reflections from the microwave resonator containing the sample, lock-in detection, and computer control. The resonator and sample chamber is a split-ring resonator formed by plating 1-5 microns of silver onto a quartz tube. The permanent magnet design consists of an open U-shaped yoke with rectangular cross-section, two opposing cylindrical permanent magnets with amorphous iron pole pieces (e.g. Metglas), and copper wound coils to provide a modulated magnetic field ramp.
U.S. Pat. No. 4,888,554 issued Dec. 19, 1989 discloses an electron spin resonance spectrometer that detects both the absorption and dispersion signals caused by magnetic resonance, by using in phase (I) and quadrature (Q) mixers. The preferred embodiment uses a microwave circulator connected to the resonant cavity; for example, a loop-gap resonator. An automatic frequency control loop (AFC) is disclosed to servo the microwave source to the cavity resonant frequency.
Other prior art electron spin resonance spectrometers for other purposes than the present invention include U.S. Pat. No. 5,142,232 issued Aug. 25, 1992, U.S. Pat. No. 5,389,878 issued Feb. 14, 1995, and U.S. Pat. No. 5,465,047 issued Nov. 7, 1995. U.S. Pat. No. 5,142,232 discloses a spectrometer design intended to provide an inexpensive ESR system with reduced weight. A permanent magnet is provided with a moveable yoke for adjustment of the magnet field. One pair of permanent magnets is attached to a stationary yoke, and a second, moveable yoke in a parallel magnetic circuit provides mechanical adjustment of the field. Carrier suppression techniques are shown in U.S. Pat. No. 5,389,878 to reduce the carrier power reflected from the resonator, which may improve spectrometer sensitivity, depending on the noise properties of the microwave source. U.S. Pat. No. 5,465,047 shows yet another ESR spectrometer, which uses frequency sweep of the microwave source and resonator, and a fixed permanent magnet. The tunable resonator described in U.S. Pat. No. 5,465,047 is a cylindrical waveguide cavity resonator with a moveable end plate for frequency adjustment. The resonator end plate is driven by a motor.
Microwave Cavities for Prior Art ESR—Structures and Usages
Eddy-current shielding of the audio frequency modulation field is well known in the art of electron spin resonance, and typically requires special construction techniques for the cavity design. U.S. Pat. No. 5,596,276 issued Jan. 21, 1997 uses non-uniform metal thicknesses in the construction of a rectangular waveguide cavity to reduce eddy current shielding by the metal surfaces. More commonly, thin layers of electroplated metal are used to define the microwave resonator surfaces, while providing minimal shielding of audio frequency fields. An exemplary method for building a loop-gap resonator, disclosed in U.S. Pat. No. 4,435,680 issued Mar. 6, 1984, is to machine the resonator elements from MACOR® ceramic, deposit a conductive seed layer by a chemical silvering process, and electroplate silver or copper onto the seed layer to a thickness of several microns.
Several types of apparatus have been used for handling fluids in electron spin resonance experiments. Dielectric loss is of particular importance for liquid samples containing water and requires special techniques. One type of cavity adapted to aqueous samples is shown in U.S. Pat. No. 3,931,569 issued Jan. 6, 1976. Another type of cavity with a fluid handling apparatus is disclosed in U.S. application Ser. No. 10/197,236 filed Jul. 15, 2002 and another is said parent application.
The novel ESR microwave system structures of said parent and the present invention, unlike the prior art, are specifically designed for the purposes and objectives of the invention; the present and parent application microwave ESR cavity systems both directly measuring peroxy radicals in the fluid passed through the preferred embodiment of the parent application (using mechanical deformation RF sweeping of the cavity resonator frequency, and the present continuation-in-part invention using a fixed cavity resonator RF frequency and sweeping the magnetic filed external and internal of the cavity.